How is your server performing routing? And do you have the server plugged into the WAN port of your router? What do you mean 3rd nic card to router? Does the server have 3 of them? Or are they from 3 separate computers talking to router?

the server has 3 nic cards i want to hook my cable modem to it directly and then from the server to the wireless router and out to the other computers.but when i do this i cant connect to the server from my desktop for file sharing so i put a 3rd nic card in it to go back to the router and give access to my files.